The pulsed dye laser

A typical dye laser cavity of the Hansch design [8, 9] is shown in Fig. 2. Such systems are typically pumped by pulsed lasers with a pulse length of 

This type of laser produces output pulses which are typically between 1 and 10 ns duration and are well suited to provide initial excitation in the study of the decay of excited states and other transient effects in small molecules. Many fundamental processes, however, occur on a time scale much shorter than the 1—10 ns resolution available with dye lasers of the type discussed above. These processes, such as the relaxation of large biological molecules and dyes in solution, exciton decay and migration in solids, charge-transfer and other non-radiative transfer processes between molecules, and many more, take place on a picosecond time scale. 

Therefore very narrow excitation pulse widths are necessary, for example, to measure sub-nanosecond relaxation times. A number of methods for generating picosecond laser pulses have been devised and several reviews of these techniques are available [10, 11]. 

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The overall conceptual layout of the pulsed dye laser LGS system is shown in Fig. 18. A thermally insulated room located on the dome floor houses much of the laser system to minimize vibrations on the telescope and the heat dissipated within the dome. The enclosure houses 6 frequency-doubled Nd YAG pump lasers, the DM0, the associated laser electronics and diagnostics, the... 

Figure 18. Layout of the pulsed dye laser guide star system at the Keck observatory.

A typical example of the pulsed dye laser excitation is the beam experiment shown in Fig. 3.4 in which Na atoms in a thermal beam are excited in two steps from the ground state 3s to the 3p state with a yellow dye laser photon and from the 3p state to a high lying ns or nd state with a second, blue photon.21... 

The simplest method to obtain high-resolution spectra is to replace the pulsed dye laser with a CW single-mode dye laser. As Steimle and co-workers have demonstrated in a series of beautiful experiments, this... 

A pulsed dye laser is also used for measurement of liquid-phase samples, because of its wide tunability. For example, Cu(II) is determined by using Pb(II)-tetrakis (4-N-methylpyridyl)porphinetetra-p-toluene sulfonate a sharp Soret band appears at 422 nm (s= 1.5 x lO lmol cm ). However, this approach is less successful because of a poor background subtraction capability, which is ascribed to pulse-to-pulse instability of the pulse energy of the pulsed dye laser. 

All other resonator components are similar to those of the pulsed dye laser configuration shown in Figure 4.10. 

Richards KA, Garden JM (2000) The pulsed dye laser for cutaneous and nonvascular lesions. Semin Cutan Med Surg 19 276-286... 

Fig. 9. A versatile set-up to detect photon echoes in an optical fiber at low temperatures. The pulsed dye lasers can be used independently or in a master-slave configuration. Dye laser 1 used in conjunction with the optical delay line can generate a ir/2 - ir sequence or dye lasers 1 and 2 can be triggered to produce the proper pulse train. Combination of the above allows one to observe stimulated echoes echoes remain trapped in fiber for detection. In the above BS, beam splitter A, attenuator E.O., electro-optical shutter and T, are synchronizing triggers. After Broer et al. (1986).

The pulsed dye laser, pumped by a ruby laser, was the first dye laser, realized already 1966 independently by Schafer [1.161] and Sorokin [5.162]. In these early days of dye laser development giant-pulse ruby lasers, frequency-doubled Nd glass lasers and nitrogen lasers were the main pumping sources. All these lasers have sufficiently short pulse durations Tp < Tjc which are shorter than the intersystem crossing time constant Tic(Si- Tj). 

These limitations have recently been eliminated using solid-state sources of femtosecond pulses. Most of the femtosecond dye laser teclmology that was in wide use in the late 1980s [11] has been rendered obsolete by tliree teclmical developments the self-mode-locked Ti-sapphire oscillator [23, 24, 25, 26 and 27], the chirped-pulse, solid-state amplifier (CPA) [28, 29, 30 and 31], and the non-collinearly pumped optical parametric amplifier (OPA) [32, 33 and 34]- Moreover, although a number of investigators still construct home-built systems with narrowly chosen capabilities, it is now possible to obtain versatile, nearly state-of-the-art apparatus of the type described below Ifom commercial sources. Just as home-built NMR spectrometers capable of multidimensional or solid-state spectroscopies were still being home built in the late 1970s and now are almost exclusively based on commercially prepared apparatus, it is reasonable to expect that ultrafast spectroscopy in the next decade will be conducted almost exclusively with apparatus ifom conmiercial sources based around entirely solid-state systems. 

A pulsed dye laser may be pumped with a flashlamp surrounding the cell through which the dye is flowing. With this method of excitation pulses from the dye laser about 1 ps long and with an energy of the order of 100 mJ can be obtained. Repetition rates are typically low - up to about 30 FIz. 

Lick Observatory. The success of the LLNL/AVLIS demonstration led to the deployment of a pulsed dye laser / AO system on the Lick Observatory 3-m telescope (Friedman et al., 1995). LGS system (Fig. 14). The dye cells are pumped by 4 70 W, frequency-doubled, flashlamp-pumped, solid-state Nd YAG lasers. Each laser dissipates 8 kW, which is removed by watercooling. The YAG lasers, oscillator, dye pumps and control system are located in a room in the Observatory basement to isolate heat production and vibrations from the telescope. A grazing incidence dye master oscillator (DMO) provides a single frequency 589.2 nm pulse, 100-150 ns in length at an 11 kHz repetition rate. The pulse width is a compromise between the requirements for Na excitation and the need for efficient conversion in the dye, for which shorter pulses are optimum. The laser utilizes a custom designed laser dye, R-2 perchlorate, that lasts for 1-2 years of use before replacement is required. 

Alster TS,McMeekin TO (1996) Improvement of facial acne scars by the 585 nm flashlamp-pumped pulsed dye laser. J Am Acad Dermatol 35 79-81... 

The Doppler-selected TOF technique is one of the laser-based techniques for measuring state-specific DCSs.30 It combines two popular methods, the optical Doppler-shift and the ion TOF, in an orthogonal manner such that in conjunction with the slit restriction to the third dimension, the desired center-of-mass three-dimensional velocity distribution of the reaction product is directly mapped out. Using a commercial pulsed dye laser, a resolution of T% has been achieved. As demonstrated in this review, such a resolution is often sufficient to reveal state-resolved DCSs. 

Figure 4. The sample cell arrangement in the DCSHG experiment, where the sample solution was inserted between two glass slips (lop), and the optical design for the DCSHG dispersion experiment, where the compressed H gas medium was pumped by a tunable pulsed dye laser source for Stokes generation by stimulated Raman scattering (bottom). (E° is the static electric field.) Key beam guiding prisms P, Stokes...

The first dye laser generates 10-ps, 2-pJ, 365-nm pulses that pump a microscopic distributed feedback dye laser (DFDL) producing Fourier transform hmited 0.7-ps pulses at 616 nm. These DFDL pulses are amplified in two stages to give 100-pJ, diffraction-limited pulses. 

Excitation spectra have been of considerable use recently in studying both hydration numbers (by lifetime measurements) and inner-sphere complexation by anions (by observing appearance of the characteristic frequencies for e.g. the Eu3+ 5D0-+ 7F0 transition for the different possible species). Thus using a pulsed dye laser source, it was possible to demonstrate the occurrence of inner sphere complexes of Eu3+ with SCN, CI or NO3 in aqueous solution, the K values being 5.96 2, 0.13 0.01 and 1.41 0.2 respectively. The CIO4 ion did not coordinate. Excited state lifetimes suggest the nitrate species is [Eu(N03)(HzO)6,s o.4]2+ the technique here is to compare the lifetimes of the HzO and the corresponding D20 species, where the vibrational deactivation pathway is virtually inoperative.219 The reduction in lifetime is proportional to the number of water molecules complexed.217 218... 

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